Glutamine can be synthesized by various tissues such as skeletal muscles, liver, and adipose tissue. However, research indicates that glutamine is conditionally essential when the metabolic demand for glutamine exceeds the amount available in the free glutamine pool and that which can be provided by de novo synthesis. For example, during exercise or other times of metabolic stress (e.g. fasting, severe injury, illness, etc.), the demand for plasma glutamine markedly increases. For instance, various cells of the immune system such as the lymphocytes and macrophages depend on glutamine as a primary fuel source, and thus the demand for glutamine increases when an immunological response is mounted.
Methods for using glutamine have been described in the art. European Patent No. 672 352 describes various solutions containing a glutamine-rich peptide preparation. U.S. Pat. No. 5,849,335 proposes a composition and method for providing glutamine to a human or animal using carob germ protein hydrolysate.
Despite the availability of free glutamine (L-glutamine), supplementation of foods with free glutamine has a number of limitations. For example, free glutamine is unstable at high temperatures or under certain conditions associated with food processing. Compositions comprising free glutamine cannot be sterilized or further processed at high temperature and/or high pressure, for example, in the form of a canned food, without destroying the free glutamine. There is, therefore, a need for nutritional food compositions that provide supplemental glutamine.